EGU2020-4738
https://doi.org/10.5194/egusphere-egu2020-4738
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Alternative approach for works controlling stony debris flows

Carlo Gregoretti, Matteo Barbini, Martino Bernard, and Mauro Boreggio
Carlo Gregoretti et al.
  • Università di Padova, TESAF, Padova, Italy (carlo.gregoretti@unipd.it)

Many sites of the Dolomites are threatened by channelized debris flows: solid-liquid surges initiated by the entrainment of large quantities of sediments into the abundant runoff at the head of channel incised on fans, can dramatically increase their volume along the downstream routing. This is the case of the Rovina di Cancia site where solid-liquid surges forming in the upper part of the basin can increase their volume up and over 50000 m3, seriously impacting the downstream village of Borca di Cadore. The debris-flow channel ends just upstream the village that in the past was hit by four debris flows (three in the recent years) that caused victims and destructions. Control works built until now are not sufficient to protect the village from high magnitude debris flows and a definitive solution calls to be planned. Present works are a flat deposition area, 300 m downstream the initiation area, an open dam under construction downstream it, and  two retention basins at the end of the channel. Between the open dam and the upstream retention basin, there are the rest of eight check-dams made of gabions, built in the 60s and progressively damaged or destroyed by the debris flows occurred after their construction. This series of check-dams limited the entrainment of solid material and the occurrence of localized scours. The initial plan is the substitution of the check-dams with concrete structures and the widening of the dowsntream retention basin through the raising of high elevation embankment downstream it and the following demolition of the actual dyke. Finally, a channel crossing the village and national route on the valley bottom will deliver the fluid phase from the widened basin to the Boite river. All these control works have a very high cost for construction and maintenance and severely impact the village with the presence of a non-negligible residual risk. These drawbacks call for an alternative solution that is searched looking at to the morphology. Downstream of the open dam and on its right side, there is a deep impluvium that ends on a large grass sloping area. The novel solution requires the construction of a channel through the right high bank that deviates the debris flow into the impluvium. The impluvium, widened through the excavation of the surrounding slopes, is closed at the outlet by  an open dam. Downstream the open dam, a channel will lead to a retention basin, where most of storage volume is obtained from the excavation of the grass sloping area, limiting the elevation of the dykes At the end of this basin an open dam will deliver the debris-flow fluid part to a channel passing under the national route and joining the Boite river. Such a solution composed of a deviatory channel, two retention basins (the deep impluvium and that excavated on the sloping grass area) and the channels between and downstream them, has quite a lower costs of construction and maintenance, eliminating the impact on the village because occupying uninhabited areas without interrupting the main roads.

How to cite: Gregoretti, C., Barbini, M., Bernard, M., and Boreggio, M.: Alternative approach for works controlling stony debris flows, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4738, https://doi.org/10.5194/egusphere-egu2020-4738, 2020

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Display material version 1 – uploaded on 03 May 2020
  • CC1: Comment on EGU2020-4738, Guillaume Piton, 04 May 2020

    Dear Carlo,
    Thanks a lot for this very interesting contribution. From the aerial picture you show slide #6, it seems that the torrent bed is quite wide in the reach equipped with check dams between the two debris basins. I was wondering how much of the debris flow volume is recruited/depostied in this reach? The numerical results seem to suggest that their is a depositional trend on the check dams. Is-it systematically the case or do you also sometime observe in the field debris flow growing by recruiting material previously deposited on check dams? 

    It is a matter of dynamic equilibrium between material carried by extreme and routine events but we lack good quality observations on this question to my knowledge. I would appreciate if you find time to discuss this point during this EGU or later.

     For interested readers, I also recommend the very comprehensive paper by the same team on the same torrent describing the model and other protection options:

    M. Bernard, M. Boreggio, M. Degetto, et al., "Model-based approach for design and performance evaluation of works controlling stony debris flow with an application to a case study at Rovina di Cancia (Venetian Dolomites, Northeast Italy)", Science of the Total Environment, https://doi.org/10.1016/j.scitotenv.2019.05.468

    Thanks again!

    Best

    Guillaume 

    • AC1: Reply to CC1, Carlo Gregoretti, 04 May 2020

      dear Guillame

      we are just submitting a paper that in part is centered on the issue you raised. The comparison between dod of two events shows some reaches where an alternation of erosion and deposition occurs after each debris-flow event. Actually the original gabion check-dams built in 60s are destroyed and solid-body check dams are planned. The new dams should contribute to locally stabilize the bed avoiding erosion phenomena that increase the sediments volume transported by debris flows. 

      thank you very much for your "high value" observation

      Carlo

       

       

      • CC2: Reply to AC1, Guillaume Piton, 05 May 2020

        Great! I look forward reading this new paper!